1. Field of the Invention
This invention relates to techniques for monitoring etch rate on semiconductor or other wafers during processing in an etch chamber.
2. Description of the Prior Art
Conventional approaches to etch rate monitoring for semiconductor wafers during processing illuminate the repetitive patterns on the wafers through windows into the etch chambers and use photodetector devices to monitor changes in diffraction patterns from repetitive features. Such conventional devices are extremely pattern dependent and therefore relatively complicated to setup, maintain and use. Such conventional devices are quite sensitive to alignment, do not provide satisfactory penetration deep into small features and have poor signal to noise ratio because only a few diffraction orders are collected and processed.